The occurrence subtype and significance of haemopoietic inhibitory T cells (HIT cells) in myelodysplasia: an in vitro study.

This study examines the occurrence, subtype and possible significance of haemopoietic inhibitory T cells (HIT cells) in patients with myelodysplasia (n = 21), acute myeloblastic leukaemia (n = 8) and in normal subjects (n = 13) using an autostimulary CFU-GM stem cell assay. HIT cells were detected when colony numbers increased by 30% or more following T-lymphocyte subpopulation ablation. HIT cells occurred in 28% of the MDS patients, were always CD8-positive and never occurred in the normal subjects. Sequential studies in MDS patients with HIT cells and treated with low dose Ara-C showed no correlation between occurrence of these cells and clinical outcome. HIT cells appear to be a clinically irrelevant manifestation of the cell dysfunction associated with MDS.